Starter for pool-type tubes



Aug. lo, w37. J. M. CAGE 2,089,174

STARTER FOR POOL-TYPE TUBES Filed May 11, 1935 Inventor: John M. Cage ,A

0 j 2 .a by F/I/WMAM i5 to prevent the attainment of this desired con- This is held in pIODer DOsition by a :depending l5 20 erable change in the 'starting potential required. threugh apIeSS i3 t0 makeCOIiiaCt With a metallic no Parenteel Aug. 1o, tot? ,2,909,174

UETE STABS PATENT OFFIE STARTER FOR POOL-TYPE TUBES John M. Cage, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York l Application May 11, 1935, Serial No. 20,964

Claims. (Cl. Z50-27.5)

My invention relates to pool-type tubes in teror of the envelope through a glass to metal Which an arc discharge is controlled by a startseal 6. ing electrode projecting below the surface of the At the top of the envelope is provided a posipool. More particularly, my invention provides tive electrode or anode l, made of graphite, 5 a starting electrode of such configuration that mOlybdenlim 0r a COIIeSpOndng heat-resisting 5' the potential required to initiate the arc dis- Conducting material. This is shown suspended charge is rendered substantially independent of by means of a conductor 8 of high current cavariations in the pool level. pacity which is also provided with an external For many of the applications in which conconnection 9 suitably sealed to the envelope stem. trolled mercury pool tubes are used, it is of In contact with the mercury and PrOjeCting le extreme importance that starting shall occur at below its surface, I have provided a starting eleca definite potential point with respect to each trode body l COmPOSed 0f a SemirCOIlduClirlg cycle of the alternating input voltage. .As a pracmaterial such as tungsten v01` SiliCOn Carbide7 tical matter, however, a number of factors tend suitably combined with clay 0I* a Similar binde?- stancy. It is well known, for example, that varia- Portion 0f a rigid COIldllCtOr ll- ThiS latter eletions in the level of the mercury pool produced ment is surrounded for a portion 0f its length by either byV external vibrations or by the conditions a glass tubulation l2 t0 protect it from Condensaof the main discharge may bring about a considtion of mercury or graphite, and is taken out I have found that if the portion of the startcap I4 mounted on the tubular extension 3. ing electrode which projects below the mercury Referrirlg tme ritariculary tto gOZ itn lvill surface be tapered in a manner which may be be seen t a e s ar ing e eC I0 e 0 y iS predetermined from the electrical characteristics mounted in a Suitable retainer i6' @Ondlletingly 0f the electrgde body, the effect 0f mercury level fitted Ol'll'IO the eleCIOde Stem. The retainer lll` 25 variations on starting voltage win be nuiiined. turn is welded or sweeed into goed Contact with AFor most of the practical electrode materials the vthe supporting Conductor! I The starting elecrequired taper will take the form of a,v concave trode l0 is clearly shown as terminating at its cone, f lower end in a concave conical surface of revolu- The novel features which I consider to be charl'fiOn- The downwardly convergent tip thus 3o acteristic of my invention will be pointed out ffliormed iS pesiliorc. sotthaltJ it1 pioicts prty with particularity in the appended claims and a 0V@ an par Y eOW he @Ve 0 e C3# 0 e may bo fully understood upon reference to the pool during the normal operation of the discharge following specication and drawing in which Fig. device lis a partially diagrammatic illustration of the E01' a' more Complete understanding 0f the' 35 arrangement in which my improved electrode is manner of Operation of the tubes With Which my to be employed; While Fig 2 is a detailed View invention is concerned,Ihave illustratedatypical partly in section of the starting electrode itself; circuit arrangement for such 9' tube' A.S Shown Figs. 3, 4 and 5 are graphical representations of a Condutor n 1s Connected from (.me 51de .of an various relationships which illustrateand explain alterna'tmg urrelt-source tp lead-m 5 Wmoh as 40 the nature of my invention above explained is 1n electrical contact with the Referring more particularly to Fig 1 r'have mercury pool. The other'side of the alternating must ted l t b current rvoltage supply 1s connected by conra a mercury p00 u e. Compnsmg an ductor I8 to the anode in series with a load I9.

elfmga'ted Sea1ed-enve10pe l provided .at each end The latter is illustrated conventionally as a re- 45 with stem portions 2 of reduced diameter. A Sistonoo but may consist of any typo of intertubular extenswn 3 1s Shown proieetmg laterally mittently operating mechanism such for example froIm iorrlie 1side of th; enveflo near its basse. as a spot-Welding device. A smoothing condenser n e ower por ion o t e enve ope is col- 20 is shown shunting the direct current load I9 lected a quantity of mercury 4 whose surface level for the purpose of eliminating irregularities in 50 is necessarily variable with the tilting or vibrathe current supply. tion of the tube, or with evaporation of mercury The starting electrode l0 is also connected to from the pool. The mercury may be connected to the anode terminal through a current-limiting an external source of potential by means of a resistor 22 and a unidirectional current-translead-in conductor 5 which is brought to the inmitting device 23. This is shown as a two-ele- 55 ment thermionic discharge tube, but may alternatively comprise an oxide lm rectifier, or equivalent element, capable of passing current only when the mercury pool is at negative potential 5 with respect to the anode. The constants of the tube I and the starting circuit are such that when the alternating current potential has reached a limiting value in such a direction that the anode becomes the positive electrode, current l passing from the starting electrode I0 into the mercury pool will initiate a, discharge. This is a phenomenon familiar to those skilled in the art and is described in an article by J. Slepian appearing in the Transactions of the A. I. E, E. l for 1933, vol. 52, page 693.

The magnitude of the current required to cause a discharge to take place is variable with several factors as will be hereinafter more fully explained. This variation is not in itself a matter of critical importance, however, since a considerable change in starting current may usually be permitted without serious consequences.

The external potential required to give rise to a sufficient starting current, on the other hand, must frequently be kept constant or within closely conned limits. This is true, for example, if the load device to be served by the main discharge is a spot welder, as suggested above. In such a case, it is extremely important that the arc-discharge be initiated only when the alternating line potential, and consequently the starting potential, has reached some exactly predetermined positive Value. Only in this way can the duration of the power impulse transmitted through the welding contact be regulated accurately. A deviation from such constancy of operation will result in a weld which is defective because of the application of either too much or too little heat, as the case may be.

Because of its poorly conducting characteristic the electrode body l0 acts as a resistance element in series with the starting circuit, the valuey of which changes in dependence on the length remaining above the surface of the mercury. Consequently, if starting electrodes of constant diameter are used, variations in the mercury level will correspondingly Vary the starting potential required to send a given amount of current into the mercury pool. 'I'his effect is shown graphically by curve A of Fig. 3 which represents -observed variations in external starting potential obtaining with a straight electrode as plotted against deviations in mercury level from an arbitrary normal line. Since fluctuations of this type lead to irregularity in operation as above explained, it is highly desirable to provide means of eliminating them.

It has been found that the amount of starting current, as distinguished from voltage, required to initiate a discharge between the main electrodes of a mercury pool tube depends to a large extent on the diameter of the starting electrode at its line of contact with the mercury surface. I have observed experimentally that a decrease or increase in such diameter results in a corresponding decrease or increase in the amount of starting current needed. In Fig. 4 I have shown the nature of this relationship as determined for the electrode material used in obtaining the data plotted in Fig. 3. The curve B illustrates the variation of starting current With electrode diameter at the line of contact, other factors being held constant.

Because of this inherent quality of the mercury pool starter it is possible, and my invention contemplates, that the tip of the starting electrode may be given a calculated form such that the effect of variations in mercury level on the starting voltage will automatically be compensated. In other words, an increase or decrease in necessary starting current will be balanced by a corresponding change in series resistance so that the total voltage drop remains unchanged.

The nature of the electrode configuration required to accomplish this result will be a function not only of the starting current characteristic but also oi the external circuit constants, and the specic resistance of the particular electrode body, but may be determined empirically for any given material. Alternatively, to the extent that the relationship between starting current and contact diameter is capable of being expressed mathematically, the corresponding electrode contour which will result in constant voltage starting may be computed exactly by setting up and solving the equations dening the desired conditions. For electrode substances within any practical range of specific resistivities the appropriate shape will be that of a concave conical surface of revolution as described above.

As exemplary of the manner in which my invention is to be applied, I have shown in Fig. 5 a graphical outline of the shape determined as proper for the tip of an electrode having the starting current characteristic shown in Fig. 4. The electrode is also chosen to have a specific resistivity equal to that of the test electrode used in connection with curve A of Fig. 3. By a comparison of Figs. 4 and 5 it will be seen that a rise in the mercury level will so increase the electrode diameter at the line of contact that a greater starting current will be required. On the other hand, the series resistance of the electrode body l0 will necessarily diminish in accordance with the change in the dimensions of the resistance path. These two eiects will, under the conditions stated, offset one another so that the required starting potential will remain constant. curve C of Fig. 3 illustrates this result and affords a comparison with the voltage-mercury level characteristic obtained' with a straight electrode.

I have described my invention as being especially applicable to mercury pool tubes, but it will be obvious that its utility extends to other liquid conductors such as gallium which are suitable for use as cathode materials.

The invention of a downwardly convergent discharge-initiating electrode is claimed broadly in application, Serial No. 74,653, led April 16, 1936, in the name of Hobart E. Rowe, and is not intended to be claimed herein except as improved by the use of a concave conical or equivalent form as disclosed in the foregoing. However, while I have shown a particular embodiment of my invention, many modifications may be made without departing from the invention, and I aim in the appended claims to cover all such modifications as fall within the true spirit and scope of the preceding disclosure.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In an electric discharge device, an anode, a mercury cathode, and a starting electrode supported above said cathode and having a portion thereof depending into permanent contact with said mercury, said portion comprising a downwardly convergent body of semi-conducting material bounded by a concave conical surface of revolution which projects partly above and partly below the mercury level.

2. In an electric discharge device, an anode, a pool-type cathode, a starting electrode supported above said cathode pool and having a tip portion depending into permanent contact therewith, and a conductor connected with said starting electrode for impressing a discharge-initiating potential thereon, the tip portion of said starting electrode comprising a semi-conducting body bounded by a downwardly convergent concave surface of revolution whereby variations in the line of contact of said pool with said body are prevented from substantially affecting the potential required to be impressed on said starting electrode to initiate a discharge.

3. In a discharge device, an anode, a. pooltype cathode having a variable surface level, a discharge-initiating electrode of semi-conducting material supported above said pool and having a downwardly convergent tip projecting partly above and partly below the level of the pool during normal operation vof the device, said electrode tip being so formed that a change in resistance of the starting current path .due to variations in level of said pool will be compensated by a change in the diameter of the line of surface contact of said electrode with said pool whereby the potential required to be impressed on the electrode to initiate a discharge is maintained substantially constant.

4. In a discharge device, an anode, a pooltype cathode having a variable surface level, a semi-conducting electrode having a downwardly convergent tip projecting below the surface of the pool during normal operation of the device, and means for impressing a starting potential on said electrode, said electrode tip being so formed that a change in starting current due to variations in the line of contact of said tip with said pool will be compensated by such a change in the dimensions of the current path that the re' quired starting potential is maintained substantially constant.

5.`In a discharge device, an anode, a pooltype cathode and a semi-conducting starting electrode having a downwardly convergent tip portion depending into permanent contact with the surface of said pool, the shape of said tip portion being so related toI the specic resistance of the electrode material that variations in the line of Contact of the pool with the electrode are prevented from appreciably affecting the potential required to be impressed on the starting electrode for initiating a discharge between said anode and cathode.

JOHN M. CAGE. 

